Two new bighorn herds will be established with fresh transplants in the Hells Canyon area this winter, part of a long-term effort to fill vacant wild sheep habitat there.
About 40 bighorns are expected to come from the same Canadian herd that provided the most recent Hells Canyon transplants. The expanding Canadian herd is reaching its carrying capacity in a region with no hunting, making extra sheep available for shipment to Hells Canyon.
Transplants and health research are part of the Hells Canyon Initiative, an effort to bring back wild sheep in an area which includes portions of Idaho, Washington and Oregon. It is funded primarily by the Foundation for North American Wild Sheep (FNAWS). The foundation has committed $10 million over 20 years to bring wild sheep back in the region.
Wildlife Research Biologist Frances Cassirer explained that sheep in the project area, which includes the Willowa Mountains of Oregon, are increasing slightly. About 780 bighorns live in 15 herds. The new transplants are not intended so much to increase the number over all as it is to establish new herds where the sheep habitat is suitable but vacant.
Health research represents an important focus in the Hells Canyon sheep project, especially since a die-off of sheep in the canyon during the winter of 1995-96. Some 300 bighorns, about 30 percent of the herds, were lost to respiratory disease. Biologists moved 72 sheep to the Idaho wildlife health lab at Caldwell during the die-off in an attempt to develop a way to halt disease losses, but animals at the lab and in the wilds continued to die anyway. Disease research efforts have continued and increased in the years since.
Newly established herds are doing well and expanding rapidly. Herds affected by the die-off are not. The reasons for this difference remain the subject of research involving several current studies. The Hells Canyon herds are not alone among bighorn populations showing productivity problems and research in Hells Canyon may eventually be useful in other parts of North America.
The herds that are not growing suffer low levels of recruitment - the lambs are not surviving in large enough numbers to raise herd numbers. A 1997 trial of a vaccine did not help.
Since then, biologists have looked again at the habitat and are currently convinced there is no reason it will not support large numbers of bighorns, as it did when Europeans arrived here. "We feel the potential for a large, thriving bighorn herd is here," Cassirer said.
Researchers have also considered the effects of predators on Hells Canyon bighorns and do not believe predation is the limiting factor. Cassirer noted that dead lambs are often found intact without any indication that predators had touched them. Biologists have, in fact, been surprised at how little predation there is on the Hells Canyon herds.
What the biologists are seeing is sick lambs, juvenile sheep with running noses and coughing, that lag behind the rest of the groups. When they do necropsies, studying the corpses of dead sheep, they see pneumonia. The question is why some herds are so susceptible.
Cassirer expects to do several years of research to learn the answers. A couple hundred sheep will be radio-collared and observed closely. Researchers in universities and other institutions will help in learning how disease works in bighorns.
"Between the laboratory work and our intensive field work, we hope to shed some light on the situation," Cassirer said, "and to share that light with wildlife researchers wherever bighorns fail to thrive in good habitat."